Clearly, some students have more aptitude than others.
Having said that, tell me if I am on the right track; I think that the amount of time children are exposed to French is a factor, be it in the company of a teacher or through follow-up provided by parents. In addition, today's technology makes it possible to increase the amount of exposure to French. Overall, being exposed to another language for 1,200 hours makes it possible to achieve very interesting results.